1. Field of the Invention
This invention relates to precision voltage references for producing a fixed d-c output voltage. More particularly, this invention relates to such a reference formed on an IC chip and providing an output voltage which is compensated for changes in ambient temperature.
2. Description of the Prior Art
A wide variety of devices and techniques have been used for developing reference voltages. One of the most common elements employed for that purpose is the well-known Zener diode which has the property of producing a substantially constant voltage when connected with a reverse-polarity supply voltage. It is known, however, that the Zener voltage varies with changes in temperature. Although such changes are relatively small, they are nevertheless significant where precision applications are involved. In addition, further small errors are introduced by the temperature sensitivity of conventional circuitry such as amplifiers and gain resistors used with Zener diodes to produce a suitable output voltage.
One technique for minimizing the Zener voltage variations with temperature is to operate the Zener at a current where its temperature coefficient (TC) is at a minimum. This however does not provide good stability over a wide range of temperatures. Zener output characteristics are non-linear with temperature, and operating at the minimum TC does not account for such non-linearities. Another approach to the problem is to use an on-chip temperature stabilizer to hold the chip temperature at a pre-set value, such as 90.degree. C. This is unsatisfactory due to excessive power consumption and also because of unreliability and inaccuracy beyond the pre-set temperature value. Accordingly, there has developed a strong need for a precision reference which avoids the problems presented by prior art devices.